This invention relates generally to a medical instrument test unit and more particularly to a test unit which is adapted to check the ground continuity and leakage current of a medical instrument, the leakage current portion of the system being adapted to check the unit under selectable standards.
In modern hospitals, the treatment, care, and monitoring of patients is accompanied by a widespread use of electrical equipment. In the use of this equipment, many hazards may arise such as the shocking of certain patients which are hypersensitive to electrical shock. This is particularly acute in the case of cardiac patients wherein electrical equipment is in the greatest use. Further, the use of certain gasses in operating rooms and the like have created an explosion hazard, which explosion could be caused by the discharge of a piece of equipment having a different potential than, for example, an adjacent piece of equipment with which it may come into contact. Thus, a necessity has arisen for providing test equipment to ensure that the continuity and leakage characteristics of the medical equipment is within manufacturing standards.
Many types of test equipment have been marketed to test various types of monitoring equipment. For the most part, this equipment has involved the use of meters and the like to indicate to the user whether the equipment under test is within manufacturing standards as far as leakage current and ground continuity is concerned. Further, while the use of indicating meters provides the user with an accurate reading of the leakage current and ground continuity condition of the equipment under test, it has necessitated the education of the user personnel to the peculiarities of the equipment under test insofar as limits of acceptable continuity and leakage current are concerned. Accordingly, it has been found desirable to provide test equipment which is of the go - no go type wherein lamps are illuminated in accordance with the conditions of whether the equipment is within standards or not. Further, it has been desirable to provide variable standards whereby the same lamps will be utilized to indicate a go or no go condition in accordance with the standards which the user has set into the test equipment.
The system of the present invention is particularly adapted to provide an indication of the acceptable condition of the equipment under test insofar as ground continuity and leakage current is concerned. Further, the equipment of the present invention provides a simple method for testing the test unit itself to ensure that it is operating properly. As a further consideration, the unit of the present invention includes a simple switch which varies the standards under which the leakage current is tested to vary the test depending upon whether the equipment is to be used in a critical service area within the hospital, for example in the intensive care area, or whether the equipment is to be used generally throughoout the hospital and not in the intensive care area. Further, the unit includes a simple test switch which is adapted to test the operability of the leakage circuit to determine if it is operating properly and test points on the exterior of the cabinet are provided to verify the correct operation of the continuity circuit.
Referring to the general details of the system, the test equipment is plugged into a suitable source of alternating current potential and permitted to warm-up for a preselected period of time. The equipment under test is then plugged into a socket provided on the test equipment to establish a circuit between the test equipment and the equipment under test. The test equipment includes a circuit for testing the continuity of the ground circuit of the equipment under test wherein a probe connected to the continuity circuit is pressed against the metallic frame or chassis of the equipment under test. This establishes a circuit whereby the impedance of the equipment under test is compared to a fixed impedance by means of a comparator circuit. If the ground impedance of the equipment under test exceeds a certain limit, a flip flop circuit is set to drive a red warning lamp. If the ground impedance is within the set limit, the flip flop circuit will drive a green lamp to indicate that the impedance is within limits. Further, the test equipment includes a leakage detector circuit which is connected in circuit with the equipment under test. Alternating current is fed to the equipment under test through the a.c. prongs of the plug 58 (FIG. 2) when mated with the corresponding female portion of socket 40 which is supplied alternating current from the source supplying energy to the test unit. If a fault occurs, the leakage current flows through a resistor connected in the input circuit of the leakage detector circuit. This current flowing through the resistor will establish a voltage which is fed to a precision rectifier through a variable limit gain control switch which establishes whether the equipment is to be tested against a critical standard or a general standard. The output of this gain control circuit is fed through the precision rectifier to the input of a dual input comparator circuit which is capable of sensing either positive or negative leakage currents. If the system is within limits, as established by the gain control circuit, the flip flop circuit will drive a green lamp which indicates that the system is within acceptable limits. If the leakage current exceeds the set standard, the flip flop circuit will drive a red warning lamp. In this way the operator is warned that the leakage current through the equipment is excessive for the particular use to be made of the equipment.
The system also includes a means for testing the operation of the circuit whereby preslected impedances are connected to the input circuit of the continuity checking circuit, one impedance causing the energization of the green lamp and the other impedance causing the energization of the red lamp, the two impedances establishing the range for the go and no-go conditions.
The leakage current detector is checked by means of a test switch mounted on the face plate or panel of the unit cabinet, the switch being a center position, toggle-type switch. When the switch is thrown in one direction, a source of potential is connected to an input of the leakage detector circuit to upset the balance of the circuit such that the dual input comparator will provide an output signal indicating that the leakage is excessive. This will cause the red warning lamp to be illuminated. On the other hand, when the switch is thrown to the opposite position, a ground potential is fed to the input circuit of the precision rectifier to upset the signal levels on the dual comparator to illuminate the green indicator lamp.
Accordingly, it is one object of the present invention to provide an improved continuity and leakage test apparatus.
It is another object of the present invention to provide an improved test apparatus for checking the leakage current and ground continuity of medical instrumentation.
It is a further object of the present invention to provide an improved continuity test circuit for use in conjunction with testing the ground continuity of medical equipment.
It is another object of the present invention to provide an improved leakage test circuit for use in conjunction with testing the amount of leakage current flowing in a medical instrument.
It is still another object of the present invention to provide an improved test unit of the type described above which has improved self-checking characteristics.
It is still another object of the present invention to provide an improved test apparatus such as the type described above which provides a means for varying the limits of the leakage test circuit.
Further objects, features and advantages of the present invention will become apparent upon reading the description and claims, and upon studying the accompanying drawings in which: